Filter element that has a thermo-formed housing around filter material

ABSTRACT

A filter cartridge ( 5 ), suitable for attachment to a respiratory mask, has a housing that includes an air inlet ( 27 ), an air outlet ( 39 ), and filter material ( 17, 19 ) through which air to be filtered travels through when passing from the inlet to the outlet. At least part of the housing includes a sheet material ( 23 ) that is thermo-formed around the sides of the filter material.

The present invention relates to a filter element that is suitable foruse, for example, in a respirator, an air filtration unit, and otherfiltering apparatus.

BACKGROUND

A filter element often needs to be replaceable so that when it reachesthe end of its useful life, it can be removed from the filteringapparatus in which it is used and can be replaced by a new filterelement. Filter elements are commonly in the form of a cartridge, thehousing of which may be provided with some form of attachment mechanismthat enables the cartridge to be fitted in, and removed from, thefiltering apparatus in which it is used. In other cases—for example,certain types of respiratory masks—the filtering apparatus is intendedto be discarded when the filter element reaches the end of its usefullife, and, in those cases, the filter element can be an integral part ofthe filtering apparatus.

Filter cartridges usually are assembled by first forming the housing andthen inserting a filtering material into the housing—see, for example,U.S. Pat. Nos. 4,592,350, 5,063,926, 5,736,041, 6,277,178, and6,248,280; and DE-A-197 00 340. As illustrated in some of thesedocuments, the housing can be formed in two parts that are closed afterthe filtering material has been placed in position. Respiratory masksthat have filter elements as integral parts of the masks have also beendescribed, for example, in U.S. Pat. Nos. 2,922,417, 2,922,418,3,861,381, and 4,790,306, and in EP-A-0 218 348.

Sorbent particles such as activated carbon are commonly used inrespirators as gas or vapor filters. The filters generally areclassified according to the manner in which the sorbent material issupported in the filter and include packed bed filters, loaded nonwovenfilters, loaded foam filters, and bonded sorbent filters.

In packed bed filters, the sorbent particles are constrained in acontainer by compressive forces imposed on and transmitted through theparticle bed by rigid grids and screens that cover the inlet and outletareas. Packed bed filters tend to be cylindrical, have constantthickness or bed depth, and have a planar inlet and outlet. To fill thecartridge, the adsorbent particles typically are poured through screensthat scatter the particles as they fall, creating a level bed packedsubstantially to maximum density. The compressive forces from theconstraining grids and screens restrain particle movement to minimizeflow channeling through the packed bed.

An example of a packed bed filter is shown in U.S. Pat. No. 4,543,112.This patent discloses a sorbent filter assembly made by sequentiallyplacing a first resilient perforated plate, a first retention filter, asorbent bed, a second retention filter, a second resilient perforatedplate, and a cover within the cylindrical portion of a canister shell.The cover is forced downwardly to compress the sorbent bed and toresiliently spring bias or stress the first resilient perforated plate.While the parts are held together under compression, an annular edgeportion of the cylindrical shell is rolled into a circumferentiallyextending groove on the canister cover to hermetically seal andmechanically hold the parts together in their assembled and compressedrelationship.

The necessity for this number of parts and processing steps introducescomplexity as well as weight, bulk, and cost. A further problem isexperienced when a packed bed respirator is combined in series with aparticulate filter for use in environments containing particulates aswell as vapor hazards such as in paint spray applications. In thissituation, the retaining grids and screens may create nonuniform airflowpathways within the particulate filter, resulting in reduced utilizationof the filter media and increased pressure drop therethrough.

Loaded nonwoven webs that contain sorbent particles in the intersticesbetween the fibers forming the web have been disclosed in the filteringface mask art. An example is shown in U.S. Pat. No. 3,971,373. Loadedfoams also have been disclosed that contain adsorbent particlesdispersed within and bonded in the foam structure. U.S. Pat. No.4,046,939 describes a carbon impregnated foam for protective clothingagainst noxious chemicals. Both loaded nonwoven webs and loaded foamstructures are edge sealed to the respirator component to preventunfiltered air from bypassing the filter. Known sealing means includeadhesives, such as disclosed in U.S. Pat. No. 5,063,926, and gaskets orsealing rings, such as disclosed in U.S. Pat. No. 5,222,488. Loadedstructures generally suffer from having a lower sorbent particle densitythan the packed beds.

A significant advance over the packed beds technology and loaded websand foams was the invention of bonded sorbents. In bonded sorbenttechnology, the sorbent particles are molded into a unitary structureusing polymer particles that bind the sorbent particles together. Bondedsorbent structures eliminate the need for additional supportingstructures, as are necessary in packed beds. An example of a bondedsorbent structure is disclosed in U.S. Pat. No. 5,033,465 (see also U.S.Pat. No. 6,391,429 B1). Bonded sorbent structures have been sealed tothe respirator using an adhesive—see, for example, U.S. Pat. No.5,078,132; or by injection molding—see, for example, U.S. Pat. No.4,790,306.

SUMMARY OF THE INVENTION

The present invention provides a new filter element that in briefsummary suitably comprises or consists essentially of (a) a housing thathas at least one inlet and at least one outlet; and (b) a mass of filtermaterial that is contained within the housing such that a fluid to befiltered passes through the at least one inlet, the filter material, andthe at least one outlet; wherein at least part of the housing comprisesa sheet material that is thermo-formed around at least part of the massof filter material to prevent passage of fluid between the filtermaterial and the sheet material so that the fluid passes through thefilter material before exiting the housing.

The present invention also provides a method of making a filter element,which in brief summary comprises the steps of: (i) providing a mass offilter material; (ii) providing a thermo-formable sheet material; and(iii) thermo-forming the sheet material around at least part of the massof filter material to encapsulate the filter material and prevent thepassage of fluid between the filter and sheet materials, thus preventingthe passage of fluid through the filter element other than along afiltering path through the filter material.

Relative to the filter elements and cartridges that have been known inthe art, the present invention can allow filter elements, such as filtercartridges for respirators, to be manufactured using relatively fewcomponents. Further, such filter elements can be made using relativelyfew manufacturing steps. A housing, into which a mass of filter materialmay be contained, can be produced through a thermo-forming step thatenables a wall of the housing to contact the filter material to preventpassage of fluid between the filter material and the housing sidewall.The housing, thus, can be easily and inexpensively manufactured whileproviding a sealing means for ensuring—when the filter element is usedin a respirator—that essentially all inhaled air passes through thefilter element. The thermo-formed sheet material also may act as aretaining means for securing the mass of filter material to the housing.These features can enable a filter cartridge to be produced for arespirator, which cartridge is relatively light in weight, possessesminimal parts, and is relatively easy to manufacture.

The term “thermo-formed” means that the sheet material has been heatedand shaped while still at an elevated temperature. The sheet materialmay have been shaped, for example, by the application of a vacuum (knownas vacuum-forming), by the application of pressure (known aspressure-forming), between shaped molds (known as match-mold-forming),or in any other suitable way.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, embodiments of the invention are described withreference to the accompanying drawings, in which:

FIG. 1 is a side view of a respiratory half-mask 1 that is provided withfilter cartridges 5 in accordance with the invention;

FIG. 2 is a front view of the mask 1 of FIG. 1, showing the filtercartridges 5 and headbands 7, 8 removed from the face piece 2;

FIG. 3 is a front view of one of the filter cartridges 5 of the mask ofFIG. 1;

FIG. 4 is a rear view of the filter cartridge 5 of FIG. 3;

FIG. 5 is a side view of the filter cartridge 5, taken in the directionof the arrows 5—5 of FIG. 3;

FIG. 6 shows a cross-sectional view of the filter cartridge 5, takenalong lines 6—6 of FIG. 4;

FIG. 7 shows a tray component 21 that forms the base of the filtercartridge 5 of FIG. 3;

FIG. 8 is a view of the inside of the tray component 21 of FIG. 7;

FIGS. 9 to 12 illustrate, diagrammatically, the steps of a method ofmaking a filter cartridge in accordance with the present invention;

FIGS. 13 and 14 are cross-sectional view similar to FIG. 6 of modifiedfilter cartridges;

FIGS. 15 and 16 are cross-sectional view of components of another formof a filter element 49A, 49B in accordance with the invention;

FIG. 17 shows a cross-sectional view of a filter cartridge formed fromthe components illustrated in FIGS. 15 and 16;

FIG. 18 is a view from the attachment side of the cartridge of FIG. 17,taken in the direction of the arrows 18—18;

FIGS. 19 and 20 are, respectively, a perspective view and across-sectional view of yet another form of filter element in accordancewith the invention; and

FIG. 21 shows a respiratory hood that incorporates a filter element inaccordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 2 show one form of a respiratory half-mask that is intendedto fit over the nose, mouth, and chin of the wearer. The mask 1comprises a face-piece 2 that may be produced by being injection moldedfrom a soft, compliant material (for example, a rubber material) andthat has an inturned cuff (not visible in the drawings) around itsedges. When the mask is worn, the cuff forms a seal against the wearer'sskin. The face piece 2 defines an interior gas space that is locatedbetween the wearer's face and the face piece 2 when the mask 1 is beingworn. The face-piece 2 has a central portion 3, intended to extend overthe bridge of the wearer's nose, in which is mounted an exhalation valve4. On opposing sides of the exhalation valve 4, the face-piece supportsinhalation valves (not visible) over which filter cartridges 5 aremounted filter cartridges 5. At the sides of the face-piece areattachments 6 for upper and lower headbands 7, 8 (only those for theupper headband being shown) that form part of a head harness, whichharness also includes a cradle 9, fashioned to fit on top of thewearer's head. The filter cartridges 5 may be releasably attached to themask by bayonet fittings. The bayonet fittings are not visible in FIG.1, but one part of one fitting is indicated at 10 in FIG. 2.

In use, the headbands 7, 8 are adjusted to fit the head of the wearerand to hold the mask 1 against the wearer's face. When the wearerbreathes in, air is drawn into the mask 1 through the filter cartridges5 and then through the inhalation valves in the cheek portions of theface-piece 2. When the wearer breathes out, air is expelled from themask through the exhalation valve 4 located in the central portion 3 ofmask body 2. The two filter cartridges 5 of the mask 1 are identical andare constructed as described below with reference to FIGS. 3 to 8.

As shown particularly in FIGS. 3 to 6, a cartridge 5 comprises a housing15 that contains a mass of filter material. The filter material mayinclude a layer of particulate filter material 17 that is disposedadjacent to one major surface of a thicker layer of a vapor-sorbing (maybe an adsorbent or absorbent or both) filter material 19. The outermajor face of the filter material 17 may be covered with a protectivescrim material 17A. The other major face of the sorbing filter material19 (which too maybe covered by a scrim material 19 to protect it) islocated in a tray-shaped base 21 that forms one part of the cartridgehousing 15. A sidewall that has sheet material 23, forming the remainderof the cartridge housing 15, is thermo-formed around and preferablyencapsulates the sides of the two layers of filter material 17, 19 andthe base 21 and a flange margin 25 that is disposed on the outer,scrim-covered major face of the particulate filter material 17. Theflange 25 extends radially inward towards the center of the filtercartridge from the housing sidewall. The term “encapsulate” means thatthe sheet material encloses the mass of filter material enough toaccomplish the objectives of producing a filter element that avertsbreak-through of unfiltered fluid through the filter element. The sheetmaterial 23 is adhered to the margin 25 of the outer major face of theparticulate filter material 17 and also to the base 21, and thusfunctions not only to encapsulate part of the mass of filter material17, 19 but also to hold the filter material 19 in the base 21. Theexposed area 27 of the outer major face of the particulate filtermaterial 17—that is, the area inside the margin 25, not covered by thesheet material 23—constitutes an inlet in the housing 15 of the filtercartridge 5 and is covered by a scrim material that serves to protectthe filter material. The base 21, described in greater detail below withreference to FIGS. 7 and 8, provides an outlet 39 for the filtercartridge 5 and a plenum chamber 37 between the outlet and the adsorbingfilter material 19.

Air enters the filter cartridge through the inlet 27 and passes along afiltering path through both the particulate filtering material 17 andthe vapor-sorbing filter material 19 before it enters the chamber 37from where it can pass through the outlet 39, the associated inhalationvalve, and then into the interior gas space defined by the face-piece 2.The close contact between the thermo-formed sheet material 23 of thecartridge housing 15 and the sides of the mass of filter material 17,19, prevents air, which air is drawn into the filter cartridge 5 throughthe inlet 27, from by-passing the filter material (referred to as“breakthrough”) by leaking around the sides of the latter, and therebyavoiding being filtered as it flows through the cartridge. The term“prevents” as used in this document, thus, means that thermo-formedsheet material substantially precludes breakthrough along the side(s) ofthe filter material. There may be some air that does indeed pass throughthe filter material at this location, but the air that does so makessufficient contact with the filter material so that the amount is not solarge that a significant quantity of air goes unfiltered and poses arisk to the safety or health of the wearer. During this inhalationprocess, the chamber 37 serves to evenly distribute the pressure dropacross the whole area of the filter material 19 to avoid prematurebreakthrough of the inhaled air through the filter material. When thewearer breathes out, the outlet 39 of the filter cartridge 5 is closedby the associated inhalation valve so that exhaled air cannot leave theface-piece 2 through the filter cartridge but is expelled insteadthrough the exhalation valve 4 in the central portion 3 of the mask 1(see FIG. 1).

In the filter cartridge shown in FIGS. 3 to 6, the air inlet 27 may bedefined by the aperture 42 in the sheet material 23, and the air outlet39 can be located in the pre-formed base tray 21. As a modification, theair inlet 27 could also be formed in a pre-formed housing component,with the thermo-formed sheet material 23 being applied against the sidesof the filter material 17, 19. Essentially any form or construction ofthe inlet, outlet, and housing is contemplated in accordance with thepresent invention so long as the air can pass through the filter mediawithout encouraging substantial breakthrough to occur.

FIGS. 7 and 8 show the housing base 21 separated from the filtercartridge 5. The side walls 29 of the base 21 are stepped or tiered toform an internal ledge 31 that supports the vapor-sorbing filtermaterial 19 in a position in which it is spaced apart from the internalbottom surface 33 of the base. Upstanding ribs 35 on the bottom surface33 provide additional support for the vapor-sorbing filter material 19and ensure the presence, within the base 21 of the chamber 37 betweenthe bottom surface 33 and the filter material. An aperture 39 in thebottom of the base 21 constitutes the outlet in the housing 15 of thefilter cartridge 5 and is separately provided with one part (not shown)of a bayonet fitting that enables the filter cartridge 5 to bereleasably-attached to the face-piece 2 of the respiratory mask 1 (FIGS.1 and 2). As shown in FIG. 4, cross bars 39A may be provided in theaperture 39—by, for example, a component that is a push fit in theaperture—to furnish support for an inhalation valve in the face-piece 2when the cartridge 5 is attached to the latter.

The particulate filter material 17 can be of essentially any type knownto be suitable for use in respirators for removing particulate materialfrom inhaled air. Preferably, for reasons described below, the filtermaterial is self-supporting. An example of a suitable particulate filtermaterial is available under the trade name “Filtrete” from 3M Company ofSt. Paul, Minn., USA. The particulate filter material can be made fromwebs of electrically-charged microfibers such as melt-blown microfibers.See, for example, U.S. Pat. Nos. 6,406,657 B1, 6,375,886 B1, 6,119,691,and 5,496,507. The fibers also can be fibrillated electrically-chargedfibers—see U.S. Pat. No. Re. 30,782 and Re. 31,285. Further, the fiberscan have fluorine atoms at their surfaces to improve their oily-mistresistance. See, for example, U.S. Pat. Nos. 5,432,175 B1, 6,409,806 B1,6,398,847 B1, and 6,397,458 B1.

The vapor-sorbing filter material 19 can be of any type known to besuitable for use in respirators for removing noxious vapors from inhaledair. Like the particulate filter material, the vapor-sorbing filtermaterial also preferably is self-supporting. Examples of suitablevapor-sorbing materials are bonded-sorbent materials such as bondedcarbon and sorbent-loaded web materials such as carbon-loaded non-wovenweb materials. Various bonded-sorbent materials, and methods for theirpreparation, are described in U.S. Pat. Nos. 5,033,465 and 6,391,429 B1.Various sorbent-loaded web materials, and methods for their preparationare described in U.S. Pat. No. 3,971,373.

The base 21 (FIGS. 6-8) of the filter cartridge can be formed fromessentially any material known to be suitable for forming a housing of afilter cartridge for a respirator. Most typically the base is formedfrom a polymeric material by, for example, a thermo-forming (e.g.vacuum-forming) or an injection molding process. A suitable material forthe base 21 is a polypropylene film or thin sheet material.

The use of a bayonet connection to attach the filter cartridge 5 to therespirator face piece 2 is not essential, and other forms of attachmentcould be used with consequent modification, if necessary, to the form ofthe outlet aperture 39 in the bottom of the base 21. Variousarrangements for attaching filter cartridges to respirator face piecesare described in U.S. Pat. No. 5,579,761, to which reference may be madefor further information.

The sheet material 23 that forms the remainder of the cartridge housing15 can be essentially any thermo-formable material that is known to beto be suitable for a housing of a filter cartridge of a respirator. Mosttypically, the sheet material 23 is a thermo-formable polymeric film orsheet (including multi-layer polymeric film materials), but it could,for example, be a laminate material that includes layers ofnon-polymeric film materials, for example metallic or woven materials. Asuitable thermo-formable material is a polypropylene film. Examples ofcommercially-available thermo-formable materials include “Simona 1 mmPP-DWST” obtained from Ensinger Ltd of Llantrisant, Wales; and “Borealis1 mm BEC 5012” and “Borealis 1.5 mm BEC 5012” obtained from Bay PlasticsLtd, of North Shields, England.

FIGS. 9-12 illustrate a method of making the inventive filter cartridge,in which components corresponding to those appearing in FIGS. 3 to 6carry the same reference numerals. A piece of particulate filtermaterial 17 and a piece of vapor-sorbing filter material 19, both cut toan appropriate shape are placed in the already-formed base tray 21,which is then located on the plate 40 of a vacuum-forming machine, overan opening 41 through which a vacuum will be pulled (FIG. 9A). As shownin FIG. 9B, an aperture 42, slightly smaller than the outer major faceof the filter material 17 is cut in the sheet material 23, and a pieceof scrim material 43 is placed over the aperture and welded, around theperiphery of the aperture to the sheet material. The sheet material 23is then placed in position in the forming frame 44 (FIG. 10) of thevacuum-forming machine, the platen 40 having first been raised to bringthe top surface of the filter material 17 to the level of the sheet toensure that the sheet 23 is correctly positioned with the aperture 42over the filter material. A plate 45 is then placed over the aperture 42in the sheet 23. This plate serves to protect the filter material 17when the sheet 23 is heated in preparation for the forming process andalso serves to seal the aperture 42 when the vacuum is pulled.

FIG. 11 shows a bank of heaters 46 in the vacuum-forming machine, whichare moved into position above the plate 45. The heaters 46 are activatedto heat the sheet to a soft, pliable state suitable for vacuum forming.During this phase, as already mentioned, the filter material 17 isprotected by the plate 45 against direct exposure to the heaters 46through the aperture 42. The heaters 46 are then removed, the platen 40is moved upwards slightly to press the scrim material 43 against theplate 45, and the vacuum pump (not shown) of the machine is switched onto remove air from beneath the sheet 23 through the opening 41 in theplaten 40 (FIG. 12). The pressure difference that is created between theupper and lower sides of the softened sheet 23 causes the sheet to movedown around the sides of the filter material and base tray assembly 17,19, 21. More specifically, because the vacuum pump draws air through thesides of the filter materials 17, 19 as indicated by the arrows 47 inFIG. 12, the softened sheet material 23 can preferably move intointimate contact with, the filter materials 17, 19. The softened sheetmaterial 23 desirably adheres to the sides of the base tray 21 (asdescribed above with reference to FIGS. 3 to 6) and, to ensure that thatcan be achieved, a passage should be provided to allow air to bewithdrawn beneath the base tray 21 as indicated by the arrows 48. Such apassage can be provided by, for example, inserting a small spacer (notshown) between the bottom of the base tray 21 and the platen 40.

When the sheet 23 has cooled, the mold platen 40 is lowered away fromthe plate 45, and excess sheet material is removed from around the basetray 21, yielding a completed filter cartridge 5 that requires only theaddition of the cross bars 39A (FIG. 4) and a component by which thecartridge can be attached to a respirator face-piece.

In a filter cartridge 5 (FIGS. 1, 3-6) produced as described above, thestep of thermo-forming the sheet 23 around the filter material 17, 19(FIG. 12) may cause the sheet material to bond to the filter materials(although this is not essential). If desired, an adhesive material or aconformable sealing material can be applied to the sheet material 23before the thermo-forming step so that it will be positioned between thesheet material and the filter materials when the filter element orcartridge is completed.

FIGS. 13 and 14 show a modification to the method described withreferences to FIGS. 9 to 12. In this method, the sheet material 23 maybe thermo-formed around the sides of the two layers of filter material17, 19 and the margin 25 of the outer major face of the particulatefilter material 17 without the base tray 21. Following thethermo-forming step, the excess sheet material 23 can be cut away toleave an outwardly extending flange 23 a to which a suitably-shaped base22 can be secured (for example, by ultra-sonic welding) to provide thechamber 37 and the cartridge outlet 39. FIG. 13, in particular, shows adish-shaped base 22 that has side walls 22A and an outwardly-extendingflange 22B that is welded to the flange 23A of the sheet material 23.FIG. 14 shows a modification in which the base 22 comprises a flat sheetthat is welded, at its edges, to the flange 23A, the chamber 37 beingprovided by extending sheet material 23 beyond the filter material 19during the thermo-forming step as indicated by the reference 23B.

In yet another modification of the method illustrated in FIGS. 9 to 12,the vapor-sorbing filter material 19 and the base tray 21 may be curvedrather than planar so that the resulting filter cartridge 5 will besimilarly curved.

A method as described above with reference to FIGS. 9 to 12 can also beused to make filter cartridges that have a different construction fromthat illustrated in FIGS. 3 to 6. FIGS. 15 and 16 show,diagrammatically, two circular filter members 49A, 49B that can be madeby thermo-forming sheet material 51 around circular pieces of filtermaterial 53 and then used to produce a circular filter cartridge of thetype shown in FIGS. 17 and 18 (not to the same scale).

The filter member 49A of FIG. 15 comprises a layer of filter material 53that has a scrim cover 53A around which a polymeric sheet material 51has been thermo-formed to engage the sides 55 and a margin 57 of onemajor face of the filter material and to provide an outwardly-extendingflange 59 adjacent the other major face. The filter member 49B of FIG.16 is similar to that of FIG. 15 except that the layer of filtermaterial 53 is provided with a central aperture 61, the walls of whichare also covered with the polymeric sheet material 51 during thethermo-forming step.

As FIG. 17 illustrates the filter members 49A, 49B secured together atthe flanges 59, using, for example, a suitable spacing material 63positioned between them, to provide a filter element that has inlets 65in the outer major faces of the members 49A, 49B and an outlet at thecentral aperture 61 of the member 49B. As shown in FIG. 18, anattachment component 67 (e.g. one part of a bayonet fitting) can beattached at the aperture 61 to provide a filter cartridge that can bepermanently- or releasably-attached to the face-piece of a respiratorymask.

FIGS. 19 and 20 show a filter element suitable for use as a cabin orroom air filter, which filter element can also be made by thermo-forminga sheet material around a filter material to provide at least part ofthe filter element housing. In this case, the filter material is aparticulate filter material 69 that is tacked into a pleatedconfiguration and that is then placed over a scrim-covered aperture 71in a sheet 73 of a thermo-formable material in a vacuum forming machine(similar to FIG. 9). The sheet material is then vacuum formed around thesides of pleated filter material 69 as shown in FIG. 20 and excess sheetmaterial is cut away to leave an outwardly-extending flange 75 adjacentto the base of the filter material.

FIG. 21 shows a filter element 100 in accordance with the invention,which filter element 100 is incorporated into a respiratory hood 101that is intended to enclose the head of a wearer. In use, the hood ispreferably closed around the neck and shoulders of the wearer by a neckseal 103. The filter element 100 may be similar to that illustrated inFIG. 15 but may have a rectangular, rather than a circular shape. Thefilter element 100 may be secured over an inhalation valve in an openingin the hood by welding an outwardly-extending flange 59 of thethermo-formable sheet material 51 (see FIG. 15) directly to the hoodmaterial. An exhalation valve (not shown) may be provided elsewhere toallow exhaled air to leave the hood. In a similar fashion, filterelements in accordance with the invention may be incorporated into otherprotective garments.

In a modification to the filter element shown in FIG. 19, thethermo-formable sheet material 51, which is used in the filter element,can also be the material from which the hood itself is formed. In thisway, the filter element can become an integral part of the hood.

Although reference has been made above to the use of particulate filtermaterials and vapor-sorbing filter materials in a filter elements andcartridges in accordance with the invention, it will be understood thatother filter materials can be employed, provided that they are in a formthat permits a sheet material to be thermo-formed around them. Forexample, web materials can be loaded with particles that remove acomponent from a fluid by chemical reaction or amalgamation rather thansorption, with particles that catalyze the conversion of a noxioussubstance to a harmless form, with particles that deliver an ingredientto, rather than remove an ingredient from, a fluid. Filter elementsconstructed as described above are not restricted to use as air or gasfilters but could also be used for liquid filtration. The filterelements can be either rigid or flexible and, as already indicated, mayhave a curved form.

The thermo-formable sheet material that is used, in the embodiments ofthe invention described above, to form at least part of the housing of afilter element can be essentially any thermo-formable material that iscapable of contacting the filter material to prevent significant fluidleakage between them and thus prevent significant quantities ofunfiltered fluid from reaching the outlet of the filter element. Asalready described, the thermo-formable material may be an impermeablepolymeric film that, during the thermo-forming process, forms some formof a bond, connection, or the like to the adjacent filter material. Thismay be achieved, for example, through the use of a multi-layer film, theinner layer of which (adjacent the filter material) has a lower meltingpoint than the other layers. Depending on the construction of the filterelement, however, the use of an impermeable thermo-formable material, ora thermo-formable material that forms an actual bond to the filtermaterial may not always be necessary to prevent unfiltered fluidreaching the outlet of the filter element. In some cases, it may besufficient that the thermo-formable material is in close contact withthe filter material, or that it compresses the edges of the latter (forexample, in the case of the circular filter elements illustrated in FIG.15).

All of the patents and patent applications cited above are incorporatedin total into this document as if reproduced in full.

This invention may be suitably practiced in the absence of any elementnot specifically described in this document.

1. A filter cartridge that comprises: (a) a housing that has at leastone inlet and at least one outlet; and (b) a mass of filter materialthat is contained within the housing such that a fluid to be filteredpasses through the at least one inlet, the filter material, and the atleast one outlet; wherein the housing comprises a sheet material thathas been thermo-formed around at least part of the mass of filtermaterial to form at least a housing sidewall that assists in preventingpassage of fluid between the filter material and the sheet material sothat fluid passes through the filter material before exiting thehousing, and wherein the housing includes attachment means for securingthe cartridge to a face piece and the housing comprises a tray in whichthe mass of filter material is located, the tray having upstandinginternal ribs on its base that engage and support the mass of filtermaterial and define a space, forming an air chamber, between the base ofthe tray and the mass of filter material.
 2. The filter cartridge ofclaim 1, wherein the housing sidewall is a fluid impervious polymericmaterial.
 3. The filter cartridge of claim 1, wherein the housingsidewall is bonded to the filter material.
 4. The filter cartridge ofclaim 3, further including a sealing material between the housingsidewall and the filter material.
 5. The filter cartridge of claim 1,wherein at least one of the at least one inlet and the at least oneoutlet of the filter cartridge is defined by the thermoformed housingsidewall sheet material.
 6. The filter cartridge of claim 1, wherein themass of filter material is self-supporting.
 7. The filter cartridge ofclaim 6, wherein the mass of filter material comprises one or morelayers, the inlet being positioned adjacent an outer major surface ofthe mass of filter material and the housing sidewall being thermo-formedaround sides of the layer(s).
 8. The filter element of claim 7, whereinthe thermoformed sheet material is secured to the outer major surface ofthe mass or filter material around the inlet.
 9. The filter cartridge ofclaim 1, wherein the mass of filter material includes a vapor-sorbingfilter material.
 10. The filter cartridge of claim 9, wherein thevapor-sorbing filter material is a bonded-sorbent material or asorbent-loaded web material.
 11. The filter cartridge of claim 9,wherein the mass of filter material also includes a particulate filtermaterial.
 12. The filter cartridge of claim 1, wherein the mass offilter material comprises a layer of particulate filter materialdisposed adjacent to a layer of vapor-sorbing material, wherein airpassing along a filtering path between the inlet and the outlet of thefilter element passes through both the layer of particulate filtermaterial and the layer of vapor-sorbing material.
 13. The filtercartridge of claim 1, wherein the mass of filter material comprises apleated layer of material.
 14. A respiratory mask that comprises a facepiece that is shaped to fit over at least the nose and mouth of aperson, and at least one filter cartridge of claim 1, through whichfiltered air can be drawn into the mask.
 15. The respiratory mask ofclaim 14, wherein the filter cartridge is detachably-secured to the facepiece.
 16. A respiratory mask that comprises a face piece that is shapedto fit over at least the nose and mouth of a person and at least onefilter cartridge of claim 1, wherein the filter cartridge includes a bedof carbon that is held in position by the thermo-formed sheet material.17. A respiratory mask that comprises: (a) face piece that is adaptedfor fitting at least over a person's nose and mouth and that assists indefining an interior gas space when the mask is worn; and (b) at leastone filter cartridge that is attached to the mask body, the filtercartridge including: (i) a housing; and (ii) a mass of filter material,wherein the filter cartridge housing has a sidewall that isthermo-formed about the mass of filter material to encapsulate the massof filter material, and wherein the housing includes a plenum that hasat least one spatial conduit so that air that has passed through thefilter material can enter the plenum and pass therethrough beforeleaving the filter cartridge housing through an outlet, the air passingthrough the housing outlet then enter the interior gas space where theair may then be inhaled by a wearer of the respiratory mask.
 18. Therespiratory mask of claim 17, wherein the filter cartridge is removablyattached to the face piece.
 19. The respiratory mask of claim 17,wherein the housing includes a means for attaching the cartridge to theface piece, and wherein the housing sidewall is thermo-formed in directcontact with the mass of filter material.
 20. The respiratory mask ofclaim 19, wherein the housing sidewall is thermo-formed in directcontact with sorptive carbon filter material.
 21. The respiratory maskof claim 17, wherein the housing further includes a flange, which flangedefines an inlet to the filter cartridge.
 22. The respiratory mask ofclaim 21, wherein the housing further includes a base, the thermo-formedhousing sidewall being thermo-formed to the base.